In cutting and grinding, it is common to employ cutting and grinding oils for the purpose of extending the life of working tools such as drills, end mills, cutting tools, grinding wheels and the like, improving the surface roughness of working surfaces and raising productivity in mechanical working by increasing machining performance.
Cutting and grinding oils fall into two general categories, namely water-soluble cutting and grinding oils used by diluting surfactants and lubricant components with water, and non-water-soluble cutting and grinding oils used directly as stock solutions composed mainly of mineral oils. In conventional cutting and grinding, a relatively large amount of cutting and grinding oil is supplied to the working section regardless of the type of oil.
The most basic and important functions of a cutting and grinding oil are the lubricating function and cooling function. Generally speaking, non-water-soluble cutting and grinding oils exhibit superior lubricating performance while water-soluble cutting and grinding oils exhibit superior cooling performance. Because the cooling effect of non-water-soluble oils is inferior to that of water-soluble oils, there is usually required a large amount of non-water-soluble cutting and grinding oil, from several liters to in some cases several tens of liters per minute.
Cutting and grinding oils that are effective for improving machining performance have drawbacks from other viewpoints, typically their adverse effects on the environment. Whether non-water-soluble or water-soluble, oils undergo gradual degradation with use and eventually become unusable. In the case of water-soluble oils, for example, solution stability is lost with growth of microorganisms, resulting in separation of the components, significant fouling of the environment and unsuitability for use. In the case of non-water-soluble oils, progressive oxidation produces acidic components that corrode metal materials and produce significant changes in viscosity, also resulting in unsuitability for use. The oils also adhere to shaved chips and the like, becoming consumed and forming waste.
The degraded oils must therefore be disposed of and replaced with new oils. Oils that have been discharged as waste must be treated in some manner to avoid adversely affecting the environment. For example, chlorine-based compounds that can potentially generate harmful dioxin during thermal disposal are often used in cutting and grinding oils developed for the principal purpose of improving working efficiency, and such compounds must therefore be removed. Cutting and grinding oils containing no chlorine-based compounds have therefore been developed, but even cutting and grinding oils free of such harmful components affect the environment if their waste disposal volume is large. Water-soluble oils can also contaminate environmental waters and therefore require costly high-level treatment.
Research has been conducted recently with cooling of cutting and grinding areas by cool air blowing, instead of using cutting and grinding oils, as a means of dealing with these problems, but the lubricating performance provided by cutting and grinding oils cannot be achieved.
In light of this background, a cutting and grinding process in minimum quantity lubrication system has been developed in which a trace amount of oil at about 1/100,000-1/1,000,000 of the amount of oil used for conventional cutting and grinding is supplied to the working section together with a compressed fluid (for example, compressed air) for cutting and grinding. In such systems, a cooling effect is achieved due to the compressed air, and the trace amount of oil used allows the amount of waste to be reduced, thereby resulting in improvement in the effect on the environment that is caused by large-scale emission of waste products (for example, see Patent documents 1, 2).    [Patent document 1] WO02/083823    [Patent document 2] WO02/081605